This invention relates generally to truck bed liners and specifically, to a process for simultaneously forming and applying a plastic liner to a truck bed.
In conventional prior art processes, truck bed liners are formed with costly male and female dies or molds which are designed to mirror the surface contours of a given truck bed configuration. The singular disadvantage of this technique is that individually specialized molds must be designed for each truck bed size and/or style. It will thus be appreciated that great amounts of time, effort and expense are associated with the manufacture of a full line of truck bed liners.
In the present invention, the need for costly male and female mold structures is eliminated. Thus, a novel and inexpensive process is disclosed by which the truck bed itself serves as a female mold. This allows the formation and application of the liner in one, fairly sample and inexpensive step. Moreover, the simultaneous formation and installation of a truck bed liner according to this invention can be performed in body shops, repair shops, or the like.
According to one exemplary embodiment of the process of this invention, a relatively rigid sheet of plastic material, such as polypropylene or polyethylene or other suitable plastic, is brought into engagement with the upper surfaces of the truck bed side walls. Side walls in the context of this invention includes at least the two parallel walls extending the length of the bed and a front wall extending therebetween. The tailgate is not necessarily included. It will be understood that the sheet is oversized in relation to the horizontal bed surface per se, so as to enable the sheet to be initially supported on the side walls. A heater bed including a plurality of electrical coils designed to heat the plastic sheet to a pliable, or semi-solid state is then brought into proximity with the sheet, preferably just above the sheet, by way of an overhead crane or the like.
In order to assure close conformance with the contours of the truck bed side walls and horizontal bed, a vacuum is applied from beneath the plastic sheet while the sheet is being heated. As the sheet reaches a temperature which renders it pliable, the vacuum will draw the sheet down and into engagement with the bed. To this end, one embodiment of the invention requires that a plurality of holes be drilled or stamped in the side walls, front wall and horizontal working surface of the bed. Each hole, or aperture, is provided with a temporarily installed fitting by which a vacuum hose is placed in communication with the space within the bed area. The individual vacuum hoses are connected to a manifold which, in turn, is connected to a suitable vacuum source.
At the same time, or as an alternative means of assuring close conformance between the sheet and the bed, such close conformance, it may be desirable to apply positive air pressure above the plastic sheet. This may be accomplished by attaching or suspending air manifolds adjacent the heater bed, so that air under pressure may be distributed through nozzles provided in the manifolds across essentially the entire upper surface of the sheet.
The pressurized air above and/or the vacuum below the heated plastic sheet insures a precise "fit" of the sheet to the bed. As the sheet cools, it hardens into a tough, durable liner.
In a related aspect, it is recognized that many pick-up trucks have a double side wall construction. In such case, the apertures provided in the side walls need only extend through the inner wall to establish communication with the space between the side walls. One or more additional apertures may then be provided underneath the side walls so that a like number of vacuum hoses can be temporarily attached thereto, for the purpose of pulling a vacuum through the enclosed space between the side walls.
After installation of the liner, excess plastic material around the peripheral edges of the liner is trimmed, and the apertures, at least those on the underside of the bed, are plugged or otherwise treated to prevent corrosion.
In a preferred embodiment of the invention, the bed area is temporarily divided into two, sealed chambers so that air may be drawn from underneath the plastic sheet and air under pressure supplied above the sheet without any necessity for drilling holes in the side walls or bed surface. In this embodiment, the heater bed and pressurized air source are provided within a housing which clamps the plastic sheet to the side walls of the bed, thereby forming a substantially airtight chamber above the sheet. At the same time, the truck tailgate is temporarily replaced by a dummy tailgate which includes a vacuum hose fitting. By this arrangement, a second substantially airtight chamber, defined by the side walls, dummy tailgate and the plastic sheet is formed below the plastic sheet. As the sheet is heated to a pliable state, a vacuum is pulled through the dummy tailgate below the sheet, while pressurized air is supplied above the sheet to force the pliable or semi-liquid sheet into close conformance with all surfaces of the bed and surrounding side walls.
It should be noted that even through the sheet is originally sized to only a slightly larger dimension than the bed surface, and is thereafter clamped about the periphery of the bed, there is nevertheless sufficient material to cover the entirety of the bed and side walls in the process by reason of thinning of the sheet as it is brought into conformance with the surface contours of the bed. In other words, the size and thickness of the original sheet is chosen to insure sufficient material to cover the bed and side walls.
Vacuum pressure sufficient to achieve the desired close fitting relationship between the plastic sheet and truck bed is in the area of 18-26 in. of Hg., while the positive air pressure applied to the upper surface of the sheet is preferably about 20 to about 100 psi, well within the capability of standard air compressors.
Other objects and advantages will become apparent from an inspection of the drawings and detailed descriptions which follow.